1. Field of the Invention
This invention relates to rechargeable batteries and, more particularly, to systems for charging of rechargeable batteries and preventing charging of non-rechargeable batteries.
2. Description of the Related Art
Most conventional battery-operated consumer products utilize non-rechargeable, or primary, batteries that are available in standard battery cell sizes. Primary batteries are batteries such as carbon-zinc or alkaline batteries that must be discarded when fully discharged. Rechargeable, or secondary, batteries are batteries such as nickel-cadmium batteries that can be repeatedly charged and discharged for a significant number of cycles before they must be discarded. Most primary batteries, if subjected to the charging current provided by a charging circuit, will become damaged and will possibly damage the product or device in which the battery is placed.
Traditionally, secondary batteries have been constructed with terminals and case configurations and sizes that are incompatible with the primary batteries that can be obtained by retail customers. More recently, secondary batteries have become available with terminals and in configurations and sizes identical to those of standard primary batteries. That is, primary and secondary batteries are no longer physically distinguishable and are now interchangeable. This interchangeability makes it easy for a consumer to inadvertently place a primary battery into either a product with a battery charging circuit or a dedicated battery charger device with a charging circuit and then inadvertently attempt to recharge the primary battery.
Efforts have been underway to prevent such inadvertent charging of primary batteries. For example, U.S. Pat. No. 4,577,144 to Hodgman et al., describes a battery charger that electrically determines if a battery cell being recharged is a primary battery or a secondary battery. Charging of a primary battery cell is inhibited and charging of a secondary battery cell is permitted.
Battery chargers that electrically discriminate between a primary battery cell and a secondary battery cell incorporate a desirable safeguard, but generally are configured for recharging only a single battery cell at a time. It would be advantageous if chargers that electrically discriminate between primary and secondary batteries could recharge more than one cell at a time. The ability to charge multiple battery cells simultaneously, however, introduces the possibility of installing a mixture of primary and secondary batteries into a charging circuit. If the user attempted to charge the mixture, damage to all of the batteries could occur. Present chargers are not configured electrically to detect a mixture of primary and secondary battery cells.
It also would be advantageous to electrically determine if a battery cell were installed in a charging circuit with the incorrect polarity. Incorrect polarity also can damage battery cells. The ability to charge multiple battery cells simultaneously also introduces the possibility of installing secondary batteries with mixed polarity. Thus, it would be advantageous to charge multiple battery cells simultaneously without risking damage to the batteries or the associated product or charger due to mixing types of batteries or installing with incorrect polarities.
From the description above, it should be apparent that there is a need to provide a battery charging system that recharges multiple secondary battery cells simultaneously and prevents charging primary battery cells mixed in with secondary battery cells and prevents charging battery cells installed with incorrect polarities. The present invention satisfies this need.